> ## Documentation Index > Fetch the complete documentation index at: https://docs.withflex.com/llms.txt > Use this file to discover all available pages before exploring further. # Preview Capture Allocation > Computes how a capture would be allocated across the Checkout Session's payment methods, without executing any capture. Takes the same request body as the capture endpoint and returns the per-payment-method allocations so you can preview a split-cart capture before committing. ## OpenAPI ````yaml /openapi.json post /v1/checkout/sessions/{id}/capture_allocation openapi: 3.1.0 info: title: Flex API description: >- The Flex API powers HSA/FSA payment processing for healthcare commerce: checkout sessions, payment intents, subscriptions, customers, refunds, disputes, and eligibility. Authenticate with your partner API key as a Bearer token. All endpoints are scoped to your partner account, and test mode is fully supported via test API keys. version: 0.1.0 servers: - url: https://api.withflex.com security: - BearerAuth: [] tags: - name: Balance Transactions - name: Captures - name: Checkout Sessions - name: Coupons - name: Customers - name: Disputes - name: Events - name: Exports - name: Files - name: Invoices - name: Letters - name: Orders - name: Payment Intents - name: Payment Links - name: Payouts - name: Prices - name: Products - name: Promo Codes - name: Receipts - name: Refunds - name: Setup Intents - name: Shipping Rates - name: Subscriptions paths: /v1/checkout/sessions/{id}/capture_allocation: post: tags: - Checkout Sessions summary: Preview Capture Allocation description: >- Computes how a capture would be allocated across the Checkout Session's payment methods, without executing any capture. Takes the same request body as the capture endpoint and returns the per-payment-method allocations so you can preview a split-cart capture before committing. operationId: v1.checkout_sessions.preview_capture_allocation parameters: - in: path name: id required: true schema: examples: - fcs_01J9XR8M3K7VZ8N2YB4WJ6T0RA type: string style: simple example: fcs_01J9XR8M3K7VZ8N2YB4WJ6T0RA requestBody: description: An envelope wrapping a single checkout session object. content: application/json: schema: $ref: >- #/components/schemas/CheckoutSessionBody_for_CaptureCheckoutSessionRequest example: checkout_session: final_capture: false metadata: order_id: '8842' channel: shopify capture_metadata: order_id: '8842' channel: shopify amount_shipping: 2500 amount_discount: 2500 amount_tax: 2500 required: true responses: '200': description: >- Preview of how a capture would be distributed across the session's payment methods. content: application/json: schema: $ref: '#/components/schemas/CaptureAllocationResponse' example: allocations: - payment_method_id: fpm_01J9XR8M3K7VZ8N2YB4WJ6T0RA last4: '4242' amount: 2500 '401': description: Unauthorized content: application/json: schema: $ref: '#/components/schemas/HttpErrorOut' example: code: string detail: string '403': description: Forbidden content: application/json: schema: $ref: '#/components/schemas/HttpErrorOut' example: code: string detail: string '404': description: Not Found content: application/json: schema: $ref: '#/components/schemas/HttpErrorOut' example: code: string detail: string '409': description: Conflict content: application/json: schema: $ref: '#/components/schemas/HttpErrorOut' example: code: string detail: string '422': description: Validation Error content: application/json: schema: $ref: '#/components/schemas/HTTPValidationError' example: detail: - loc: - string msg: string type: string '429': description: Too Many Requests content: application/json: schema: $ref: '#/components/schemas/HttpErrorOut' example: code: string detail: string security: - BearerAuth: - checkout_sessions:write components: schemas: CheckoutSessionBody_for_CaptureCheckoutSessionRequest: description: An envelope wrapping a single checkout session object. type: object required: - checkout_session properties: checkout_session: $ref: '#/components/schemas/CaptureCheckoutSessionRequest' description: The checkout session payload. example: checkout_session: final_capture: false metadata: order_id: '8842' channel: shopify capture_metadata: order_id: '8842' channel: shopify amount_shipping: 2500 amount_discount: 2500 amount_tax: 2500 CaptureAllocationResponse: description: >- Preview of how a capture would be distributed across the session's payment methods. type: object required: - allocations properties: allocations: description: >- The computed capture amount allocated to each payment method. No capture is executed. type: array items: $ref: '#/components/schemas/CaptureAllocation' example: allocations: - payment_method_id: fpm_01J9XR8M3K7VZ8N2YB4WJ6T0RA last4: '4242' amount: 2500 HttpErrorOut: title: HttpError description: The error response returned when a request cannot be completed. type: object required: - code - detail properties: code: description: A short machine-readable error code identifying the type of error. type: string detail: description: A human-readable explanation of what went wrong. type: string example: code: string detail: string HTTPValidationError: description: The error response returned when request validation fails (HTTP 422). type: object required: - detail properties: detail: description: The list of validation errors, one entry per invalid field. type: array items: $ref: '#/components/schemas/ValidationErrorItem' example: detail: - loc: - string msg: string type: string CaptureCheckoutSessionRequest: description: >- Parameters for capturing funds previously authorized on a Checkout Session. type: object properties: final_capture: description: >- Whether this is the final capture. When `true`, any uncaptured authorized amount is released; when `false` (Default), the remaining amount stays authorized and can be captured by a subsequent request. `null` defaults to `false`. type: - boolean - 'null' example: false line_items: description: >- The specific line items and amounts to capture. Omit to capture the full authorized amount across all line items. type: - array - 'null' items: $ref: '#/components/schemas/LineItemCaptureRequest' metadata: description: >- Set of key-value pairs to attach to the capture for storing additional structured information. type: - object - 'null' example: order_id: '8842' channel: shopify capture_metadata: description: >- Set of key-value pairs to set on the Checkout Session's `metadata` when the capture succeeds. `null` to leave the session metadata unchanged. type: - object - 'null' additionalProperties: type: string example: order_id: '8842' channel: shopify amount_shipping: description: >- Portion of the captured amount attributable to shipping, in the smallest currency unit (e.g., `599` = $5.99 USD). type: - integer - 'null' format: int32 example: 2500 amount_discount: description: >- Portion of the captured amount attributable to discounts, in the smallest currency unit (e.g., `500` = $5.00 USD). type: - integer - 'null' format: int32 example: 2500 amount_tax: description: >- Portion of the captured amount attributable to tax, in the smallest currency unit (e.g., `175` = $1.75 USD). type: - integer - 'null' format: int32 example: 2500 example: final_capture: false metadata: order_id: '8842' channel: shopify capture_metadata: order_id: '8842' channel: shopify amount_shipping: 2500 amount_discount: 2500 amount_tax: 2500 CaptureAllocation: description: How much of a capture is allocated to a specific payment method. type: object required: - amount - last4 - payment_method_id properties: payment_method_id: description: ID of the PaymentMethod this portion of the capture is allocated to. type: string example: fpm_01J9XR8M3K7VZ8N2YB4WJ6T0RA last4: description: >- The last four digits of the card backing this payment method. `"unknown"` if the card details could not be resolved. type: string example: '4242' amount: description: >- Amount allocated to this payment method, in the smallest currency unit (e.g., `2500` = $25.00 USD). type: integer format: int32 example: 2500 example: payment_method_id: fpm_01J9XR8M3K7VZ8N2YB4WJ6T0RA last4: '4242' amount: 2500 ValidationErrorItem: description: >- Validation errors have their own schema to provide context for invalid requests eg. mismatched types and out of bounds values. There may be any number of these per 422 UNPROCESSABLE ENTITY error. type: object required: - loc - msg - type properties: loc: description: >- The location as a [`Vec`] of [`String`]s -- often in the form `["body", "field_name"]`, `["query", "field_name"]`, etc. They may, however, be arbitarily deep. type: array items: type: string msg: description: The message accompanying the validation error item. type: string type: description: >- The type of error, often "type_error" or "value_error", but sometimes with more context like as "value_error.number.not_ge" type: string example: loc: - string msg: string type: string LineItemCaptureRequest: description: Identifies a single line item to capture and how much of it to capture. type: object example: product: fprod_01J9XR8M3K7VZ8N2YB4WJ6T0RA properties: amount_to_capture: description: >- The amount to capture for this line item, in the smallest currency unit (e.g., `2500` = $25.00 USD). Omit to capture the full authorized amount for the item. type: - integer - 'null' format: int64 minimum: 0 maximum: 4294967295 example: 2500 product: type: string example: fprod_01J9XR8M3K7VZ8N2YB4WJ6T0RA description: ID of the Product identifying the line item. price: type: string example: fprice_01J9XR8M3K7VZ8N2YB4WJ6T0RA description: ID of the Price identifying the line item. securitySchemes: BearerAuth: type: http scheme: bearer bearerFormat: API Key description: Use a Bearer token to access this API. ````